package ai.zixing.mashibing.basic_class.class08;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;

// 给定一棵二叉树的头节点head，和另外两个节点a和b。
// 返回a和b的最低公共祖先 (初次交汇点)
public class Code07_LowestAncestor {

    public static Node lowestAncestor1(Node head, Node o1, Node o2) {
        if (head == null) {
            return null;
        }
        HashMap<Node, Node> parentMap = new HashMap<>();
        parentMap.put(head, null);
        fillParentMap(head, parentMap);
        HashSet<Node> o1Set = new HashSet<>();
        Node cur = o1;
        o1Set.add(cur);
        // o1Set 存放的是 o1 节点的所有祖先
        while (parentMap.get(cur) != null) {
            cur = parentMap.get(cur);
            o1Set.add(cur);
        }
        cur = o2;
        // o2 在 o1 的祖先上查找，找到就是最小公共祖先
        while (!o1Set.contains(cur)) {
            cur = parentMap.get(cur);
        }
        return cur;
    }

    /**
     * 递归查找每个节点的父节点 Map
     *
     * @param head      head
     * @param parentMap parentMap
     */
    public static void fillParentMap(Node head, HashMap<Node, Node> parentMap) {
        if (head.left != null) {
            parentMap.put(head.left, head);
            fillParentMap(head.left, parentMap);
        }
        if (head.right != null) {
            parentMap.put(head.right, head);
            fillParentMap(head.right, parentMap);
        }
    }

    static class Info {
        // 交汇点，可能是空的
        public Node ans;
        public boolean findO1;

        public boolean findO2;

        public Info(Node ans, boolean findO1, boolean findO2) {
            this.ans = ans;
            this.findO1 = findO1;
            this.findO2 = findO2;
        }
    }

    public static Node lowestAncestor2(Node head, Node o1, Node o2) {
        return process(head, o1, o2).ans;
    }

    private static Info process(Node head, Node o1, Node o2) {
        // 空树没信息
        if (head == null) {
            return new Info(null, false, false);
        }
        Info leftInfo = process(head.left, o1, o2);
        Info rightInfo = process(head.right, o1, o2);
        boolean findO1 = head == o1 || leftInfo.findO1 || rightInfo.findO1;
        boolean findO2 = head == o2 || leftInfo.findO2 || rightInfo.findO2;
        // o1 和 o2 最初的交汇点
        // 1) 在左树上已经交汇
        // 2) 在右树上已经交汇
        // 3) 没有在左树或者右树上提前交汇，o1、o2 全了
        Node ans = null;
        // 左右只能中一个
        if (leftInfo.ans != null) {
            ans = leftInfo.ans;
        }
        if (rightInfo.ans != null) {
            ans = rightInfo.ans;
        }
        if (ans == null) {
            if (findO1 && findO2) {
                ans = head;
            }
        }
        return new Info(ans, findO1, findO2);
    }

    public static Node generateRandomBST(int maxLevel, int maxValue) {
        return generate(1, maxLevel, maxValue);
    }

    // for test
    public static Node generate(int level, int maxLevel, int maxValue) {
        if (level > maxLevel || Math.random() < 0.5) {
            return null;
        }
        Node head = new Node((int) (Math.random() * maxValue));
        head.left = generate(level + 1, maxLevel, maxValue);
        head.right = generate(level + 1, maxLevel, maxValue);
        return head;
    }

    // for test
    public static Node pickRandomOne(Node head) {
        if (head == null) {
            return null;
        }
        ArrayList<Node> arr = new ArrayList<>();
        fillPrelist(head, arr);
        int randomIndex = (int) (Math.random() * arr.size());
        return arr.get(randomIndex);
    }

    // for test
    public static void fillPrelist(Node head, ArrayList<Node> arr) {
        if (head == null) {
            return;
        }
        arr.add(head);
        fillPrelist(head.left, arr);
        fillPrelist(head.right, arr);
    }

    public static void main(String[] args) {
        int maxLevel = 4;
        int maxValue = 100;
        int testTimes = 1000000;
        for (int i = 0; i < testTimes; i++) {
            Node head = generateRandomBST(maxLevel, maxValue);
            Node o1 = pickRandomOne(head);
            Node o2 = pickRandomOne(head);
            if (lowestAncestor1(head, o1, o2) != lowestAncestor2(head, o1, o2)) {
                System.out.println("Oops!");
            }
        }
        System.out.println("finish!");
    }
}
